Preparation of distannanes

ABSTRACT

Distannanes of the formula R3Sn-SnR3, wherein R represents a monovalent hydrocarbon radical, are prepared in high yield and purity by reacting the corresponding triorganotin halide with molten metallic sodium at elevated temperature in the absence of any solvent or diluent other than the reactants.

United States Patent Debreczeni et al.

[ Oct. 17, 1972 [54] PREPARATION OF DISTANNANES [72] Inventors: Eugene J. Debrecz eni; Bernard G.

Kushlefsky, both of Edison, NJ. [73] Assignee: M&T Chemicals, Inc., Greenwich,

Conn.

[22] Filed: June 18, 1971 [21] App]. No.: 154,702

521 u.s. Cl. ..260/429.7 [51] Int. Cl. ..C07f 7/22 [58] Field of Search ..260/429.7

[56] References Cited UNITED STATES PATENTS 3,311,649 3/1967 Molt et a1. ..260/4 29.7

2,965,661 12/1960 Ramsden ..260/429.7 3,027,393 3/1962 Jenkner ..'.....260/429.7 3,105,000 9/1963 Hardy ..260/429.7 3,132,070 5/1964 Lukes ..260/429.7

Primary Examiner-James E. Poer Assistant Examiner-Wertcn F. W. Bellamy Attorney-Kenneth G. Wheeless et al.

[57] ABSTRACT Distannanes of the formula R SnSnR wherein R represents a monovalent hydrocarbon radical, are prepared in high yield and purity by reacting the corresponding triorganotin halide with molten metallic sodium at elevated temperature in the absence of any solvent or diluent other than the reactants.

5 Claims, No Drawings PREPARATION OF DISTANNANES I BACKGROUND OF THE INVENTION The present invention relates to the preparation of distannanes. Distannanes have been prepared by reacting a trialkyltin chlordie with sodium in liquid ammonia. Such a process is commercially undesirable since it requires the use of high-pressure equipment.

Relatively low yields (e.g., 56 percent) of distannanes are reportedly obtained by reacting tributyltin chloride with a 20 percent excess of sodium n a hydrocarbon solvent, e.g. naphtha. US. Pat. No. 3,31 1,649 teaches that the yield of distannanes can be substantially increased by replacing the hydrocarbon solvent with a tetraalkyltin compound. The foregoing methods leave much to be desired with regard to yield, purity, and/or volume efficiency, i.e. the volume of reaction mixture required to obtain a given amount of SUMMARY OF THE INVENTION The present invention provides an improved method for preparing distannanes of the formula R SnSnR wherein R represents a monovalent alkyl hydrocarbon radical containing between two and 12 carbon atoms inclusive, said method comprising reacting a trialkyltin halide R SnX with sodium metal, wherein the improvements comprise carrying out the reaction using molten sodium metal in the absence of any solvent or diluent other than the trialkyltin halide, permitting the reaction mixture to reach a temperature between 100 and 220C., then maintaining the reaction mixture at about 200C. until the reaction is substantially complete, and then isolating the resultant distannane.

DETAILED DESCRIPTION OF THE INVENTION The reaction between sodium metal and trialkyltin halide is often highly exothermic, and it is, therefore, preferable to have about half the sodium metal present in the initial reaction mixture. Should atmospheric moisture or other impurity which is reactive with sodium be present in the initial mixture, it is preferred to employ a slight excess of sodium metal. The mixture of sodium and trialkyltin halide is heated at least to he melting point sodium, i.e., 97.5C. 'Temperatures between 170 andl80C. are preferred since at these temperatures the reaction becomes self-sustaining and the temperature often rises spontaneously to between 200 and 220C. Once the initial exothermic reaction is complete, the remaining portion of sodium may be added. It is desirable to cool the reaction mixture to near ambient temperature before the second sodium addition to minimize the likelihood of splashing, spillage, or an uncontrollable reaction, all of which could result in injury to personnel operating the equipment. After completion of the second sodium addition, the

temperature is again increased to the point where the reaction becomes self-sustaining. Following completion of this exothermic reaction, external heating is applied to maintain the reaction mixture temperature between 180-200C. for about 2 hours or longer to ensure a substantially complete reaction.

The final reaction mixture contains an insoluble sodium halide salt formed as a by-product of the reaction. The salt is separated from the liquid phase by any convenient means, i.e., by filtration. Any unreacted sodium will be coprecipitated with the salt. The solid phase should, therefore, be combined with methanol or other alcohol to eliminate the danger of fire resulting from contact between the sodium and atmospheric moisture.

The liquid portion of the reaction mixture is comprised substantially entirely of the desired hexalkylditin a hexalkyl distannane, which can be used without any additional purification. If a product of greater purity is desired, the liquid phase may bedistilled. In some instances, the hexalylditin compounds, which are waterwhite when pure, may be discolored, as a result of impurities in the starting material, i.e., the trialkyltin compound.

The yieldof desired product can often be increased by washing the sodium halide by-product with a suitable hydrocarbon solvent, e.g., cyclohexane. Alternatively, the sodium halide is dissolved in water and the solution extracted with the hydrocarbon solvent. The hydrocarbon solvent should be relatively low boiling and, therefore, readily separable from the desired product by distillation or stripping, i.e., a relatively rapid removal of the solvent under reduced pressure.

Trialkyltin halides suitable for use in the process of this invention contain up to 36 carbon atoms and include compounds such as trimethyltin chloride, tri-npropyltin chloride, tri-isopropyltin chloride, tri-n-buty1- tin chloride, tri-sec-butyltin chloride, tri-n-amyltin chloride, tri-n-hexyltin chloride, tri-n-octyltin chloride, tri-n-dodecyltin chloride, etc. Any of the foregoing compounds in which the chlorine atoms are replaced by bromine are also useful providing that they are liquids at the reaction temperature, i.e., above about C.

Since the trialkyltin halide may contain small amounts of impurities, e.g., monoalkyltin trihalides and dialkyltin dihalides, it is desirable to use a slight excess over the theoretical amount required by the stoichiometry of the reaction.

The following examples illustrate preferred embodiments of this invention but should not be interpreted as limiting the scope thereof.

EXAMPLE 1 Preparation of Hexapropyldistannane The following reagents were placed in a nitrogenfilled reaction flask equipped with a mechanically driven agitator, water-cooled reflux condenser, thermometer, and nitrogen inlet.

tripropyltin chloride 283.4 g. (1.0 mole) sodium metal (10) 12.6 g. (0.5 moles 5% excess) (cut into small chunks) The contents of the flask were gradually heated to 103C. at which point an exothermic reaction occurred and the temperature rose spontaneously to C. When the exothermic portion of the reaction was temperature increased to 1 1 1C., the reaction mixture was heated to 200C. for about 2 hours and then allowed to cool. The excess sodium was reacted by the addition of a small portion (about 25 cc.) of methanol, followed by 100 cc. eachof cyclohexane and water, the latter being added to dissolve the sodium chloride which had precipitated during the reaction. The organic phase was separated and the solvents (cyclohexane and methanol) removed by distillation. The residue weighted 208 g. (84 percent yield) and exhibited the following analysis:

tin-45.9%

chlorine-0.7%

bromine number-34.6 and 35.9 (two trials) calculated for [nC l-l Sn] tin 47.9%;

chlorine-%; bromine number--34.8%.

EXAMPLE Preparation of l-lexahexyldistannane Hexahexylditin) 1 Analysis: 1 Calculated Found tin 31.72 30.35

% chlorine 0 None found Bromine number 21.36 19.2

EXAMPLE 3 Preparation of l-lexabutyldistannane A -liter capacity reaction flask equipped with mechanically activated agitator, thermometer, and reflux condenser was charged with 1,952.9 g. (6.0 moles) of tri-n-butyltin chloride and. 82.8 g. (3.6 moles) ofsodium metal which had been cut into small pieces. The contents of the flask were then heated with agitation to a temperature between 90100C. at which time an exothermic reaction occurred and external heating was: discontinued. Thetemperature of the reaction mixture reached about 200C. Upon completion of the exothermic reaction, as evidenced by a decrease in reaction mixture temperature, external heating was applied to maintain the temperature at 200C. for 2 hours. External heating was then discontinued and the reaction mixture allowed to reach ambient temperature, at which time an additional 69 g. (3.0 moles) of finely divided sodium metal were added.

An exothermic reaction ensued upon heating the reaction mixture to C. When .the reaction subsided, the temperature was maintained at C. for 2 hours, after which the mixture was allowed to cool. Filtration of the mixture under a nitrogen atmosghere yielded 923.6 g. of a clear, yellow llqlll The $011 material was washed with heptane, after which the remaining solid was cautiously added to methanol.

The liquid from the washing was concentrated under reduced pressure to yield 487 g. of a clear, yellow liquid. The combined liquid phases weighted 1,41 1.4 g. (81.2 percent yield). The two liquids were analyzed with the following results.

In the foregoing examples the bromine number is equal to'the percent of bromine (based on sample weight). which will react with the sample. One mole of bromine is believed to react with one mole of distannane toyielcl 2 moles of a triorganotin bromide.

Although this invention has been illustrated by reference to specific examples illustrating preferred embodiments, changes therein which clearly fall within the scope of the invention will be apparent to those skilled in the art. It is, therefore, to be limited solely by the scope of the appended claims.

What we claim is:

1. A novel and improved method for preparing distannanes of the formula R Sn-SnR wherein R represents a monovalent aliphatichydrocarbon radical containing between two and 12 carbon atoms and X represents a chlorine or bromine atom, by reacting a trialkyltin halide R SnX with sodium metal, wherein the improvements comprise using molten sodium metal in the absence of any additional solvent or diluent other than said trialkyltin halide, permitting the reaction mixture to exothermically reach a temperature between about 100 and 200C., and maintaining said mixture temperature of about 200C. until the reaction is substantially complete.

2. The method of claiml wherein R is selected from the group consisting of propyl, butyl, and hexyl radicals and X is chlorine or bromine.

3. The method of claim 1 wherein the metallic sodium is added in two substantially equal portions, the second portion being added following'completion of the initial exothermic reaction.

4. The method of claim 1 wherein the sodium halide produced as a by-product of the reaction is extracted using at least one portion of a hydrocarbon solvent.

5. The process of claim 4 wherein the sodium halide is dissolved in water and the resultant solution is extracted using said hydrocarbon solvent. 

2. The method of claim 1 wherein R is selected from the group consisting of propyl, butyl, and hexyl radicals and X is chlorine or bromine.
 3. The method of claim 1 wherein the metallic sodium is added in two substantially equal portions, the second portion being added following completion of the initial exothermic reaction.
 4. The method of claim 1 wherein the sodium halide produced as a by-product of the reaction is extracted using at least one portion of a hydrocarbon solvent.
 5. The process of claim 4 wherein the sodium halide is dissolved in water and the resultant solution is extracted using said hydrocarbon solvent. 